Removal of nitrate contamination from nickel-plating solutions

ABSTRACT

A nitrate-contaminated nickel-plating bath is purified by heating the bath to between 65* and 70* C., agitating the bath and electrolyzing the bath while providing a 10 to 20 fold greater cathode area than anode area.

Unite States Patent Knight et al.

[ Feb. 8, 1972 154] REMOVAL OF NllTRATE CONTAMINATHON FROM NiCKEL-PLATING SOLUTIONS [72] Inventors: James T. Knight, Ontario, Oreg.;Parley L.

Lee, Richland, Wash.

[73] Assignee: The United States of America as represented by the UnitedStates Atomic Energy Commission [22] Filed: June 13,1969

[21] App1.N0.: 833,142

UNITED STATES PATENTS 1/1917 Hunt ..204/l02 ()TH ER PUBLICATIONSElecu'opluting Engineering Handbook. by A. K. Graham, 1962, pp. 245-246Modern Electropluling, by F. A. Lowenheim I963, pp, 293-293 PrimaryExaminer-John H. Mack Assistant ExaminerR. L. Andrews Attorney-Roland A.Anderson [5 7] ABSTRACT A nitrate-contaminated nickel-plating bath ispurified by heating the bath to between 65 and 70 C., agitating the bathand electrolyzing the bath while providing a 10 to 20 fold greatercathode area than anode area.

1 Claims, No Drawings REMOVAL OF NITRATE CONTAMINATION FROMNICKEL-PLATING SOLUTIONS CONTRACTUAL ORIGIN OF THE INVENTION Theinvention described herein was made in the course of, or under, acontract with the United States Atomic Energy Commission.

BACKGROUND OF THE INVENTION This invention relates to purifyingnickel-plating solutions and, more particularly, this invention concernspurification of a nitrate-contaminated nickel-plating solution or bath.

Nickel-plated uranium slugs are used as fuel in some nuclear reactors.The nickel plating may be performed by a standard Watts process with anall chloride bath, The standard Watts process for nickel plating is wellknown in the art as are the various types of bath compositions which maybe used with the Watts process, see Vol. 2, Metals Handbook, 8thEdition, American Society for Metals (1964), pp. 432-443. In the nickelplating of uranium, it is very important to maintain the bath purityand, in general, contamination at only a very low level is acceptable.Because of prior operations on the uranium before the slugs enter thenickel bath, various contaminants are dragged in with them. Theabove-mentioned reference sets out purification procedures effective forvarious organic and inorganic contaminants, such as iron, copper,magnesium, lead, various oils and paints. All the enumeratedpurification procedures in the Metals Handbook reference use elevatedtemperatures and elevated pHs, some use filtering agents such ascharcoal or clay and some use electrolysis.

The uranium slugs to be nickel plated have previously been in contactwith nitric acid and it is probably this contact which is responsiblefor the nitrate contamination present in the nickel-plating bath. Whilepurification procedures as enumerated above, are available for variouscontaminants, none of them reduce nitrate concentration, and they areuseless where nitrates are present in sufficient quantities to hinderoperation of the bath. A procedure for removing nitrates was reported inthe March 1966 issue of Plating magazine which electrolyzed with lowcathode areas at a pH of 0.5 and with high-current densities but such aprocess is inconvenient if the volume of additional acid required toobtain the pH is so great as to render the plating solutionunmanageable.

SUMMARY OF THE INVENTION The process of this invention comprisesmaintaining a nitrate-contaminated nickel bath between 65 and 70 C.,agitating the bath and electrolyzing the bath at its operational pH witha cathode area substantially larger than the anode area; a filtermaterial may be provided as well as a dummy plating surface for variousmetallic impurities to plate onto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT After severalineffective experiments with the prior art purification processesreported in the Metals Handbook, all of which required adding nickelcarbonate to the bath to raise the pH to between 5.2 and 5.5 prior toelectrolyzing at a cathode current density of about 5 amps/sq. ft., itwas decided to initiate electrolysis at the operating pH of the bath.The all chloride bath used in the nickel plating of uranium slugs isoperated at a pH of about 2.4 and it is at this general pH value whichthe purification procedure must start.

It was clearly'unexpected that the simple step of starting electrolysisat the operational pH rather than first raising the pH would make theremoval of nitrates possible, particularly when the fact is known thatthe pH of the bath rises during electrolysis so that at the end of thepurification the pH is about 6. Various baths contaminated with from 360to 730 parts per million (p.p.m.) of nitrates have been successfullypurified with the rocess of this invention.

The baths are eated to between 65 and C. PIlOl to purification andagitated during the purification. While purification occurs at lowertemperatures it is too slow to be practical, but agitation of the bathis required to effectively remove nitrate contamination. After the aboveconditions are satisfied, then electrolysis is started at currentdensities from about 1 mo amps/sq. ft. of cathode area, and the cathodearea is 10 to 20 times that of the anode. Up to 0.03 lbs. of activatedcharcoal (about 325 mesh) per gallon of bath may be added for heavilycontaminated baths, but if charcoal is used then the bath must befiltered. The above conditions have resulted in reduction of nitratecontamination from 730 to 70 p.p.m. and from 360 to 26 p.p.m. Theprocess also removes the usual type of impurities present in anickel-plating bath and a dummy plating surface may be provided ifmetallic ions, such as iron, copper or magnesium, are present. In allcases, it must be remembered that artificially raising the pH of thebath prior to electrolysis prevents effective removal of nitratecontamination.

If the dummy plating surface is present than the metallic ions willplate onto it and be removed from the bath. Exactly how the nitrates areremoved is not known but it is believed that they boil off as ammonia.Since the concentration of nitrates is low and the baths are open to theatmosphere it is very difficult to collect off-gases from the bath foranalysis, and the above explanation is advanced as only a possibility.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A process for reducing the nitrate concentration by approximately afactor of 10 in a nickel-plating bath utilized for the nickel plating ofuranium slugs, said bath having a nitrate contamination of at least 360p.p.m. nitrates, comprising heating said bath to between 65 and 70 C.;adding 0.03 lb. of 325 mesh activated charcoal per gallon of bath; andelectrolyzing the bath at a current density of l to 6 amps/sq. ft. witha cathode area 10 to 20 times as great as the anode area, the pH of saidbath initially being 2.4 and rising to 6 during said electrolysis whileagitating said bath during electrolysis.

